Current laws of thermodynamics may be insufficient to fully explain the behavior of living organisms, and recent experiments with human cells suggest the need for a fourth law tailored to biological systems. The established principles of physics, particularly those governing heat and entropy, are robust for idealized, non-living systems. However, life’s inherent complexity—its interconnected cells and active energy consumption—introduces factors that existing laws struggle to capture.
The Unique Disequilibrium of Life
Living systems are fundamentally out of equilibrium. Unlike inert matter, cells maintain a dynamic state through constant energy input and feedback mechanisms. This is exemplified by a cellular “set point,” where internal processes self-regulate to maintain stability, much like a thermostat. Standard thermodynamics, designed for passive systems, doesn’t easily accommodate this active behavior.
To investigate this, researchers at the Dresden University of Technology in Germany conducted experiments using HeLa human cells—a controversial cell line derived without consent from Henrietta Lacks in the 1950s. By halting cell division and probing their membranes with atomic force microscopy, they analyzed fluctuations in cellular behavior under various conditions.
The Limits of Existing Models
The study revealed that conventional thermodynamic measures, like “effective temperature,” fall short when applied to living systems. Effective temperature attempts to quantify disequilibrium similarly to how heating a pot of water increases its temperature. However, cells don’t behave in the same way. Instead, the researchers found that “time reversal asymmetry” offers a more accurate measure of disequilibrium in biological processes.
Time reversal asymmetry explores how different a process would be if run backward instead of forward. Biological processes, driven by survival and replication, inherently exhibit asymmetry, distinguishing them from reversible physical reactions. This suggests that the degree to which a system defies time’s symmetry directly correlates with its “aliveness.”
Implications and Future Research
The findings provide valuable tools for quantifying disequilibrium in living systems. Experts like Chase Broedersz at Vrije Universiteit Amsterdam emphasize the importance of precisely measuring how far a system deviates from equilibrium. Yair Shokef at Tel Aviv University notes that this study is novel in its ability to measure multiple non-equilibrium characteristics simultaneously.
The ultimate goal is to develop a fourth law of thermodynamics specific to living matter, where processes operate around a set point. Researchers are already working to identify measurable physiological indicators that could serve as the foundation for this new law.
Understanding life through thermodynamic principles requires significant further research. The ability to measure and quantify the unique disequilibrium of biological systems is a crucial step towards a more complete understanding of life’s fundamental physics.
